The present invention relates to an apparatus for forming stacks from folded printing products, such as newspapers, periodicals and the like, and to a process for operating this apparatus.
An apparatus of this type is known from DE-A-27 52 513 and the corresponding CA-A-1,091,707. A number of printing products are in each case fed in imbricated formation by means of a belt conveyor to a stack compartment, closed at the bottom by slide plates, where a preliminary stack is formed from the printing products. Then, the feeding of printing products into the stack compartment is interrupted and the slide plates are drawn apart in order to drop the preliminary stack into a receiving space of a bundle-forming unit onto a raisable and lowerable depositing table, closing off said receiving space at the bottom, or onto a preliminary stack already deposited onto said table. Then, the stack compartment is closed again at the bottom by pushing together the slide plates, so that the belt conveyor can again feed a number of printing products for the forming of a preliminary stack. The depositing table is turned, together with the receiving space, in each case after the take-over of a preliminary stack through 180.degree. about the vertical axis, in order to form a finished stack from preliminary stacks turned with respect to one another. After turning, in each case the depositing table is raised in order to compress the printing products present in the receiving space between itself and the slide plates. Subsequently, the depositing table is lowered to such an extent that the printing products no longer bear against the slide plates, so that then the next preliminary stack can be received. As soon as a complete finished stack has been formed, the depositing table is lowered completely and the finished stack is ejected from the receiving space by means of an ejecting device.
In an operation processing printing products, the printing products usually arrive continuously. In order to be able to feed these continuously arriving printing products in the necessary number in each case to the stack compartment, either the belt conveyor is assigned a gap-forming device or a plurality of successively connected stack-forming devices are provided, the stack compartments of which are supplied alternately with the corresponding number of printing products. In the case of use of a gap-forming device, the gap is determined by the time which the stacking device requires to transfer a preliminary stack to the bundle-forming unit and to close the stack compartment again by the slide plates. During this time, the continuously arriving printing products are accumulated, which can adversely affect the speed with which they can subsequently be fed to the stack compartment, and the quality of the preliminary stack. Ultimately, the processing capacity is also determined by the said time.
If in each case the number of printing products necessary for a preliminary stack is fed alternately to a plurality of stack compartments, the time during which a stack compartment cannot be fed any printing products is in turn determined by the time requirement which is needed to transfer a preliminary stack to the bundle-forming unit and to close the stack compartment again by means of the slide plates. Ultimately, the number of required stack-forming devices is also determined by this time.
There is consequently a need to minimize the time during which a stack compartment cannot be fed any printing products.
A further stack-forming device having a stack compartment which can be closed at the bottom by slide plates and in which a number of printing products are stacked to form a preliminary stack is known from EP-A-0 348 610 and the corresponding U.S. Pat. No. 5,002,456. In order that the last, respectively, of the preliminary stacks transferred to the bundle-forming unit arranged underneath the slide plates does not have to be compressed between the depositing table and the slide plates before the ejecting of the finished stack out of the receiving space, and nevertheless the necessary stability of the finished stack is achieved, this prior art teaches feeding the printing products, with the fold ahead, to the stack compartment and supporting them on the side opposite the fold in the middle region by a supporting element which can be swung into the stack compartment. The printing products in this case assume a roof-like shape in the region opposite the fold. As a result, the processing time in the bundleforming unit can indeed be shortened, but not the time for emptying the stack compartment and closing it again by the slide plates.
German Offenlegungsschrift 31 30 945 and the corresponding U.S. Pat. No. 4,445,681 disclose an apparatus for extracting the printing products conveyed at great speed by means of a gripper conveyor from the conveyed stream. In the case of the triggering device for the grippers of the gripper conveyor there is provided a stop which, upon switching on and off of the triggering device, can be moved into the conveying path of the products and out of this conveying path, respectively. The printing products extracted from the conveyed stream and retarded at the stop fall directly into a stack compartment of a stack-forming device for forming a preliminary stack.
Finally, apparatuses for forming stacks from uninterruptedly arriving printing products are known from CH-A-648 262 and the corresponding U.S. Pat. No. 4,432,685 and CH-A-566 928. The apparatus according to the two first-mentioned documents has two stack compartments which can be turned about a vertical axis and are closed off at the bottom by a raisable and lowerable stacking table which can be moved in opposed mode between a receiving position at the outlet of a conveying device, designed as a belt conveyor, and a depositing position underneath a bundle-forming unit, which can be charged from below with preliminary stacks. Provided above the stack compartments, located in the receiving position, is an intermediate stacking device, which can be switched on during the movement of the stack compartments for forming an intermediate stack from the fed printing products. This intermediate stacking device fulfils the same purpose as the gap-forming device mentioned further above, namely to store continuously arriving printing products intermediately during a time in which they cannot be fed to a stack compartment. It is also proposed in CH-A-566 928 to provide an intermediate storing device in order to store intermediately in stack form the continuously fed printing products during the time which is required to transfer a preliminary stack from a stack compartment to a bundle-forming unit arranged underneath the latter and to close the stack compartment again. The stack compartment is in this case able to be closed by an inclined grating formed by two racks which can be swung in opposite directions but in common mode. The intermediate-stacking device has a separating member which is designed like a rack and which, as soon as a preliminary stack has formed, is swung into the path of the printing products leaving the outlet of a conveying device designed as a belt conveyor, so that they cannot fall into the stack compartment. At the same time as the swinging in, a downward movement of the separating member commences. This lasts until the last printing product fed to the stack compartment for forming a preliminary stack has reached the stacked printing products and the preliminary stack has been released to pass to the bundle-forming unit by a turning of the carrying racks. In this time, there forms on the lowering separating member a partial stack, which is then dropped onto the carrying racks, without a backlog occurring in the conveying device or the feeding of the printing products having to be interrupted.
An apparatus for forming stacks of plastic bags or carrier bags is disclosed in DE-A-23 57 658. Arranged underneath a bottom which can be moved into and out of the stack compartment is an intermediate bottom, which can likewise be moved into and out of the stack compartment and the vertical distance of which from the bottom corresponds at least to the height of a finished stack. The stack forming begins on the bottom moved into the stack compartment, so that the bags or carrier bags thrown off from a conveying device have to overcome only a small drop height. Before reaching the desired stack height, the bottom is opened, so that the stack falls onto the closed intermediate bottom. As soon as the stack has been formed completely on the intermediate bottom, the bottom is moved into the stack compartment, so that the next stack begins to form on said bottom. Once the bottom has been moved in, the stack is set down, by opening the intermediate bottom, on an intermittently or continuously circulating stack belt for carrying away. Subsequently, the intermediate bottom is closed again, in order that it can receive the following stack. This known apparatus allows continuous feeding of the bags or carrier bags, but only the formation of stacks of a small height is possible.
On the basis of this prior art, it is an object of the present invention to provide an apparatus of the general type in which the time during which no printing products can be fed to the stack compartment is as short as possible.